The formula for the mirror is -
\( \frac{1}{f} \) + \( \frac{1}{u} \) = \( \frac{1}{v} \)
\( \frac{1}{f} \)+ \( \frac{1}{v} \) = \( \frac{1}{u} \)
\( \frac{1}{u} \) + \( \frac{1}{v} \)= \( \frac{1}{f} \)
\( \frac{1}{u} \) - \( \frac{1}{v} \)= \( \frac{1}{f} \)

Identify the figure which does not belong to this group -
Two inlet pipes can fill a tank in 5 and 7 hours respectively. And one outlet pipe can empty this full tank in 14 hours. If all the three pipes are opened simultaneously in a completely empty tank, then in how much time will it take to fill the tank completely?
4 \( \frac{11}{13} \)Hours
5 \( \frac{11}{13} \)Hours
3\( \frac{13}{9} \)Hours
5 \( \frac{2}{13} \)Hours